1. Field of the Invention
The present invention relates to an endoscope system and, more particularly, to an endoscope system using a pulse transformer to which a differential signal flowing through a differential signal line is inputted.
2. Description of the Related Art
Conventionally, endoscopes have been widely used in a medical field and an industrial field. In particular, in an endoscope system used in the medical field, in order to secure safety for patients, a part of a CCD driving circuit and a video signal processing circuit are mounted on a patient circuit insulated and separated from a secondary circuit.
For example, as disclosed in International Publication No. 2007/004428 and Japanese Patent Application Laid-Open Publication No. 2007-167590, an endoscope system that uses a differential signal for transmission of a signal between a patient circuit and a secondary circuit is proposed. In those proposals, the differential signal is a signal conforming to a standard of LVDS (Low Voltage Differential Signaling). For insulation, a pulse transformer is used in an LVDS transmission channel.
When external noise is mixed in a differential transmission line that transmits the differential signal, if the external noise is common mode noise, the external noise is cancelled by a subtraction in a termination circuit section. Therefore, the differential signal has a characteristic that the differential signal is robust against the external noise. Usually, a pattern on a substrate on an input side of the pulse transformer is formed such that characteristic impedance is, for example, 100 [Ω], and the common mode noise is cancelled.